Studying the influence of the physicochemical properties of lipid nanoparticles for mucosal vaccine delivery
Lipid-based nanoparticles have attracted attention as promising pharmaceutical carriers. Reports of them having inherent adjuvant properties make them particularly interesting as vaccine vectors; however, the physicochemical profile of an ideal nanoparticle for mucosal vaccine delivery remains unknown. The aim of this thesis work is to contribute a better understanding of the connection between physicochemical properties of lipid nanoparticles used as vaccine carriers and the activation of the immune response at several different levels of complexity. As combined antigen and adjuvant, we used a novel fusion protein comprising the Cholera toxin A1 subunit, combined with either the M2e or Ealpha peptide and a dimer of the D subunit of Staphylococcus aureus protein A. This fusion protein was coupled to liposomes and lipodisks with systematically varied poly(ethylene glycol) (PEG) content, protein load, rigidity and size/shape. Firstly, a detailed characterization of the biological response in vitro and in vivo, in a mouse model, to two types of fusion protein-carrying lipid particles was performed. Compared with the free fusion protein, which is in itself already an effective vaccination compound, the result showed that the non-PEGylated liposomes more efficiently induce both cell- and antibody-mediated immune responses as well as protection against a lethal virus challenge than both free fusion protein and the PEGylated liposomes. Secondly, an in vitro study was performed, focusing on elucidating the effect of the physicochemical properties of the carrier particle on processing, in particular the antigen presentation in major histocompatibility complex class II (MHC II), by dendritic cells. Out of 6 different formulations, which varied with respect to PEGylation, fusion protein load, membrane rigidity, size and shape it was found that only the DSPC-based liposome formulation, the only liposome formulation in gel phase, was able to increase antigen presentation compared to free fusion protein. Additionally, this formulation lead to an increased amount of surface-bound MHC II, indicating that the liposomes themselves might have an immunostimulatory effect, making them a promising candidate for further evaluation as a vaccine carrier with inherent adjuvant properties.